Generic Host Independent Operating SysTem

What is GHOST?

Most software developers take operating systems for granted. They view the operating system and the underlying hardware as one indissoluble entity. Only when they go through the agony of a rehost, when they must rewrite portions of their code to work with the new operating system, do they realize the difference between the two.

The goal of GHOST is to provide the most elusive of holy grails: application software independence of hardware and system architecture. It does this by hiding the details of the underlying system via a layered design.

GHOST stresses portability and flexibility. Meaning, easy transition of software between differing processors and proper communication between differing processors. By supporting both embedded and non-embedded platforms, GHOST provides a new way for writers of embedded applications to do their job.

GHOST allows application developers to begin coding in a friendly development environment such as a VAX/VMS, Sun/Solaris, or even on a PC, rather than an embedded system with the confidence that the operating system functionality is identical. When logic errors are corrected, developers can transition smoothly to less friendly embedded environments and concentrate on timing problems.

Occasionally, laboratory environments lack sufficient hardware due to cost or availability issues. Delays are costly. However, they are avoidable. GHOST allows software development to proceed. "Clusters" of processors may be built using existing systems and standard communication mediums such as ethernet. These systems need not be similiar. GHOST will provide predictable results operating on a intermediate processing environment. When circumstances allow for the acquisition of proper hardware, unit tested software will be ready for final integration with a simple recompilation.

Features

• Portable Packages. All Ada compilers and target processors are not created equal. Ada INTEGER types are not equivalent in size or range. Ada FLOAT types do not provide the same precision nor are they stored using similar formats on target processors. Big endian and little endian systems do not communicate correctly without intervention. GHOST solves these problems, providing true software portability, through Portable Packages.Portable Packages include portable types, math libraries, and conversion utilities all geared to ensure the same results on varying hosts.
• Surrogates . Surrogates are predefined, generic methods of handling input and output. Tried and true methods that applications may use and reuse.
• Heterogeneous Processing . GHOST not only runs on different processors, it provides utility services to support an on-line mixture of processor types into a single, unified system. These utilities perform tasks like word and byte swapping, floating point encoding, bit rearrangment, any types of data manipulation required to send data from one type of processor into another type and ensure that the data that an LPU recieves is properly formatted for its host processor, even tho the LPU itself does not know the type of host on which it resides. The overhead associated with this data encoding/decoding is minimal, imposing no significant degradation in run-time performance.

  Vendors of some run-time systems allow software to be ported from one system to another. GHOST is not a run time system, but an operating system that uses the run-time system to provide for combinations of processor types. This allows the user to develop code in one of our non-embedded environments but test the code as part of the fully-operating system. This drastically eases implementation by elimiating the need to debug in an embedded environment.

• Reconfiguration .
  • Loadable Program Units (LPU) . LPU's are simply executable programs, the smallest unit of software handled by GHOST. An LPU is not limited to a single task. It may contain many tasks. An LPU executes on a single processor. A single processor may execute many LPU's. In systems that do not support dynamic reconfiguration, many LPUs get combined into a single executable program. GHOST support communication between code executing within a processor and between processors. Under GHOST, an LPU does not know where it resides, where its data sources reside, or where its data consumers reside.
  • Module Management . On systems that support dynamic reconfiguration, GHOST interacts with the Ada run-time system (RTS) to invoke and terminate LPUS. It loads the program images from mass memory into local processor memory using its own memory-management algortihm, then invokes the RTS to activate the LPU as a free-running executing program.

    Leaving control of the LPU in the domain of the RTS simplifies priority scheduling of Ada tasks by allowing the programmer to assign priorities of tasks using the Ada pragmas.

  • System Management . Module Management deals with LPU control at the processor level. System Management deals with it in the system as a whole by assigning LPUs to processors. Using heuristics to detemine the resources available in each processor and the processor requirements of LPUs, System Management assigns LPUs to the processor best able to host the LPU.

    System Management also performs periodic checks of each processor to determine its health. If it determines that a processor has gone off-line, it reallocates the LPUs that had been assigned to that processor to other processors in the system.

    System Management communicates LPU load/unload commands to the Mission Managers via standard GHOST messages, and is therefore totally portable.

  • Mission Management . Module and System Management deal with LPU control. Mission Management deals with software at a higher level. It translates mission needs into a set of LPUs required to support the mission at any time. A start-up mode may have radically different software needs from a data-processing mode and those needs may differ from a shutdown mode. Mission Management determines the current software needs of the system.

    Mission Management communicates LPU load/unload commands to the System Manager via standard GHOST messages, and is therefore totally portable.

  • Embedded versus Non-embedded . Reconfiguration implementations differ between embedded and non-embedded systems. The non-embedded system approach is truly portable using a very creative Ada tasking method pioneered by American Computational. All non-embedded systems are limited to a single image, but within that image reside all of the LPUs the user mite wish to run on that processor.
    On embedded systems, we tailor the RTS interaction to hardware and compiler capabilities for enhanced performance.
• Services .
  • Messaging . GHOST supports message passing between tasks and/or LPU's. The method of transfer is not a distingusihing factor. Messages may be transfered by different communication methods, however, the same interface is utilized. Supported methods vary from Parallel Interconnect (Pi) Bus and MIL-STD-1553B to commercially available Ethernet and the shared memory network, Scramnet.
  • File I/O . GHOST supports the reading and/or writing of data files. To provide maximum hardware configuration options, File Services are designed to be independent of storage device type and location. For example, typical configurations may include (but are not limited to) an external mass memory or an internal SCSI drive.
  • Events and Semaphores . GHOST provides low overhead alternatives to the Ada rendezvous for synchronization and mutual exclusion.
  • Time . Time services are meant to supplement and enhance the standard Ada delay statement. These services provide global time, delays, and synchronous remote procedures using a higher resolution timer (when available) than typicalAda delay implementations.

Current Hosts and Features

• Embedded Hosts .
  • Westinghouse VHSIC 1750a - Reconfigurable, Multiple LPU.
    Communication:
    • PI Bus
    • Fiber Optic High Speed Data Bus
    • Mil-STD-1553B
  • Tronics JIAWG i960MX - Static Loading, Single LPU.
    Communication:
    • PI Bus
    • Mil-STD-1553B
    • Ethernet
    Tools:
    • Non-intrusive message collection,
    • Event logging.
  • CDI AN/AAYK-14 (MIPS R4400) - Static Loading, Single LPU.
    Communication:
    • FutureBus+
• Non-embedded Hosts .
  • VAX/VMS - Reconfigurable, Single LPU.
    Communication:
    • Ethernet
    • Fiber Optic HSDB
    • DTI Mil-STD-1553B
    • SCRAMNET (shared memory)
    • TCP/IP
    Tools:
    • Non-intrusive message collection,
    • Event logging.
  • Sun - Static Loading, Single LPU.
  • PC/Windows - Static Loading, Single LPU
    Tools:
    • Non-intrusive message collection
    • Event logging
    • On-line plotting configured from databases.
• POSIX-Compliant Interfaces .

Future Products and Upgrades

• Support for Ethernet on all Non-embedded Hosts.
• Support for 1553B on all Non-embedded Hosts.
• Reconfiguration for all Non-embedded Hosts.
• Reconfiguration for the Tronics JIAWG Processor.
• Support for the Westinghouse Comanche Processor.
• VME communications
• CORBA
• X-Windows and plotting
• Mixed-language (C/C++ and Fortran) LPUs

How do I learn more about GHOST?

GHOST is a fine product from the Software Specialists of
American Computational Technical Services, Inc.

For information or questions on support for additional hosts or features please contact Mike Miedlar

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